1. Field of the Invention
The present invention relates to a method for manufacturing carbon-carbon composites, and more particularly, to a method for manufacturing carbon-carbon composites, in which the densification process has been improved, to reduce manufacturing time and costs while maintaining good high-temperature properties of the finished product (e.g., brake disks) such as frictional coefficient, abrasion, thermal conductivity, thermal expansion coefficient, density, specific heat, compression and shear strength, and oxidation resistance.
2. Discussion of the Related Art
In general, a carbon-carbon composite is an essential material in a variety of high-technology applications requiring durability at very high temperatures. Research and development of its manufacture and application technologies have progressed since the end of the 1960's. Since the 1970's, carbon-carbon composites have been used in the disk brakes of jet fighters, large passenger airliners, and other aircraft due to their excellent resistance to friction, abrasion, and thermal shock. Additional applications include and the disk brakes of land transportation means such as tanks, special vehicles, rapid transit trains, and racing cars, high-temperature structures such as gas turbine blades and jet-engine parts, the rocket nozzles of launch vehicles, the re-entry surfaces of the space shuttle, the walls of fusion reactors, and electrodes and other high-temperature industrial equipment.
Thus far, improvements to the method of manufacturing carbon-carbon composite materials has focused on the production of materials having improved properties, rather than striving for reducing production cost or shortening the process time. Accordingly, production costs have remained very high, with huge investments required for manufacturing facilities.
More recently, however, the importance of cost reduction and process simplification has drawn attention. Cost reduction research has been generally achieved through one of two means: through a cost reduction in carbon fiber, which accounts for the majority of the raw material for manufacturing carbon-carbon composites, and through process simplification.
Carbon-carbon composites generally comprise carbon fiber filler and carbon matrix. The carbon fiber filler is poly-acrylonytrile-based fiber (or PAN-based fiber), pitch-based fiber, or rayon-based fiber. The carbon matrix is pitch, phenolic resin, furan resin, or pyrolytic carbon using a CVD method.
The method of manufacturing carbon-carbon composites can be basically divided into a process of producing a preform using a carbon-based fiber or fabric as the carbon fiber filler, and a process of densifying the preform to meet application criteria. The method also includes a high-temperature thermal treatment process, which is performed on the preform before densification, a high-temperature thermal treatment process after densification, and an oxidation resistant treatment to impart durability on the finished product.
Initially, the densification process used a resin char, but poor physical properties of the thus-manufactured product led to chemical vapor infiltration technology, which is widely used now. Such infiltration of carbon, however, requires a time-consuming process. Another technology, one using pitch, is also drawing attention. Rather than employing one or the other method, however, multiple processes can be combined for manufacturing the product. These technologies have been applied to real products, and the techniques used are selected based on the desired application of the ultimately produced material.
The carbon-carbon composite material produced by combining multiple processes is lightweight and exhibits good properties in terms of hot strength, specific strength, heat resistant impact, chemical resistance, and biocompatibility. The end product is applicable to environments higher than 3000° C. in an inactive atmosphere, such as the brake disks of aircraft, rapid transit trains, and other large high-speed vehicles. In manufacturing carbon brake disks for aircraft, chemical vapor infiltration is primarily used. As an alternative, a combined technology of phenolic infiltration/carbonization and chemical vapor infiltration is used.
Conventional technologies are applied when manufacturing the carbon-carbon composites by producing a two-dimensional preform laminated in a regular form using carbon fiber or carbon fabric, performing densification through a liquid impregnation process using pitch, phenol, etc., and performing thermal treatment at a specified temperature, while a three-dimensional preform is woven in the x-, y-, and z-axes using oxi-PAN fiber or PAN fiber, followed by a densification process or a chemical vapor infiltration process. The performance and physical properties of a carbon-carbon brake disk can be determined according to the processes employed. Especially, the performance of carbon-carbon composite brake produced by the chemical vapor infiltration has been highly rated.
The manufacture of two-dimensional preforms, however, is disadvantageous in that the manufacturing process requires a long lead-time and the strength is low. Meanwhile, there are as yet no successful manufacturing methods for three-dimensional preforms, though it is known that the final product is affected by fiber component ratio (reinforced along the three axes), weaving direction, and carbon fiber volume ratio.
Several publications relate to the above subject matter.
According to U.S. Pat. No. 5,688,577 (W. Novis Smith, et al.), carbon-carbon composites can be manufactured by producing a preform using a needle process after forming several layers laminated with UD fiber at 22.5°, 45.0°, 67.5°, and 90° from the x-axis, to produce a three-dimensional preform using non-asbestos based materials, and thereafter performing a densification process on the preform using chemical vapor infiltration, resin impregnation, etc.
According to U.S. Pat. No. 5,952,075 (Steven Clark, et al.), a preform can be manufactured by using a needle process after laminating with a specified thickness using fabric (plain or satin weave).
According to U.S. Pat. No. 6,077,464 (Neil Murdie, et al.), a preform can be produced with the use of Mesophase pitch, thereby producing carbon-carbon composites by performing densification through a CVD, HIP, PIC, or VPI process, or by a combination thereof.
According to U.S. Pat. No. 6,180,223 (Ronald Fisher, et al.), carbon-carbon composites can be produced by performing a densification process with chemical vapor infiltration using a preform including a susceptor foil, wherein the process is performed using hydrocarbon gas. The portion including the susceptor foil is processed by high density condition than other portion has a comparatively high thermal conductivity, thereby having higher strength than other parts, so that a part bearing the load can be improved effectively.
Korean Patent No. 1999-0061153 (Ik-hyun O H, et al.) is related to a method of manufacturing carbon-carbon composite materials by producing an intermediate molding body of carbon-carbon composites and performing impregnation/carbonization on pitch several times. Thus, a preform can be produced with an intermediate molding body. The method comprises steps of producing oxi-PAN fiber for producing oxi-PAN mats and then stitching the oxi-PAN mats.
According to Korean Patent No. 2000-0064393 (Hubbard David Andrew, et al.), a friction-interlocking device comprises a carbon-ceramic composite including carbon fiber network and a filler including silicone carbide. The carbon-ceramic composite has the structure including 35–50 wt % of carbon fiber, 14–30 wt % of free carbon, 10–28 wt % of silicone carbide, 5–14 wt % of silicone, and 5–14 wt % of silicone oxide.
Korean Patent 1999-0000133 is related to carbon-carbon composites for friction materials, such as those used for the brake disk of rapid transit trains and automobiles. Here, a method for manufacturing carbon-carbon composites comprises steps of producing a molding body by alternately laminating carbon fiber with a mixture of carbon fiber, pitch powder, and graphite powder, producing a green body by placing the molding body into a molding machine for heating and compressing, performing a first carbonization on the green body, performing a second carbonization several times by impregnating pitch on the first-carbonated material, and performing chemical vapor infiltration on the carbonated material with hydrocarbon.
When manufacturing a carbon-carbon composite brake disk using the above-mentioned processes, the manufacturing process is overly time-consuming and failure rates are high. In addition, it is difficult to meet product requirements in frictional coefficient, abrasion, thermal conductivity, thermal expansion coefficient, density, specific heat, compression and shear strength, and oxidation resistance, which are typically required of a brake disk used in the various applications as mentioned above.